It is known from Guo, Rotem, Heyman, & Weitz, “Droplet microfluidics for high-throughput biological assays”, Lab. Chip. 12 (2012), that droplets in microfluidic systems (or “microdroplets”) may be used to contain chemical or biological reactions. In these systems, the content of these droplets may be assayed by observing the fluorescence of the droplet when it passes in front of a focused laser. However, these systems do not make it possible to observe the change over time of the content of these droplets without extracting them from the microfluidic device.
The study of individualized cells in microdroplets is also known, for example from Joensson, H. N. & Andersson Svahn, H., “Droplet microfluidics a tool for single-cell analysis”, Angew. Chem. Int. Ed. Engl. 51, 12176-12192 (2012). Indeed, these microdroplets form well-defined compartments which make it possible to isolate biological samples such as cells, for example. This document especially teaches that the localization of the populations of encapsulated cells may be controlled by virtue of the accumulation of the droplets in culture chambers, in elongated channels, or else in static traps. This document also teaches that the cells may be encapsulated in functionalized hydrogels, surrounded by an oily phase.
However, the supply of nutrients or more generally of molecules of biological interest for the cells in such devices proves limited and the methods used (for example by electrofusion or picoinjection) prove complex. Consequently, these devices have numerous limits for the study of cell behavior, in particular in terms of time.
Moreover, from L. Yu, M. C. W. Chen and K. C. Cheung, “Droplet-based microfluidic system for multicellular tumor spheroid formation and anticancer drug testing”, Lab Chip (2010), a method is known for handling hydrogel microdroplets containing multicellular spheroids. According to this method, hydrogel microbeads including cells are produced in a first microfluidic system. They are then recovered and washed in a bath, before being injected into a second microfluidic system comprising traps making it possible to fix the microdroplets.
Such a method is, however, complex, necessitating two separate microfluidic systems and three devices in total. In addition, it does not enable continuous observation of the samples. In particular, it does not make it possible to observe the initial moments between the formation of the droplets and the capture thereof.